LED lighting systems can include one or more LED devices that become illuminated as a result of the movement of electrons through a semiconductor material. LED devices are becoming increasingly used in many lighting applications and have been integrated into a variety of products, such as light fixtures, indicator lights, flashlights, and other products. LED lighting systems can provide increased energy efficiency, life and durability, can produce less heat, and can provide other advantages relative to traditional incandescent and fluorescent lighting systems. Moreover, the efficiency of LED lighting systems has increased such that higher power can be provided at lower cost to the consumer.
Certain LED lighting units can include multiple different types of LEDs. For instance, an LED lighting unit can include a first string of LEDs associated with a first color (e.g. wavelength) or intensity and a second string of LEDs associated with a second color or intensity. For instance, LED lighting units used, for instance, for horticultural applications can include one or more LED strings for providing a red color light (e.g. wavelengths in the range of about 600 nm to about 750 nm) as well as one or more LED strings providing a blue color light (e.g. wavelengths in the range of about 400 nm to about 500 nm). These LED strings can be powered by a driver current from a driver circuit. In certain applications, the LED strings can be coupled in parallel, for instance, to accommodate a higher powered driver circuit. Given the different output requirements and turn-on voltage requirements of each of the LED strings, coupling the LED strings in parallel can result in a voltage imbalance in the voltage demands for the plurality of the LED strings. And since the turn-on voltage (e.g. forward voltage) can be inversely proportional to the wavelength of the LED semiconductor material, this imbalance can be especially pronounced for parallel strings of blue and red LEDs. Also, LEDs of different semiconductor materials and resulting wavelengths usually have unequal maximum drive current ratings which can necessitate that each parallel LED string be driven at a different drive current.